Passive autofocus camera systems achieve a sharp focus position by stepping through a series of focal positions frame by frame and analyzing the sharpness statistics in the image captured by the camera in each frame. The statistics allow the algorithm to determine the best focus position for the actuator to ‘move’ to. Existing systems require at least one frame taken at each focal position, and depending on the specification of the camera this can take many frames to determine the position of best focus. This leads to the poor autofocus convergence time which is undesirable to the user.
In particular, autofocus convergence time on simpler mobile phone camera systems is typically very slow. This means an unpleasant delay for the user waiting for autofocus convergence before taking the still image, which can result in missed picture opportunities.
There is a need in the art to alleviate the above drawbacks by reducing this delay.